Scaly Rustgill Identification Guide

The first impression

The setting is conifer wood in some state of decay: a spruce or pine stump greening over with moss, a rotting log on a plantation floor, a heap of old sawdust, a buried root under needle litter, or the cut end of a fallen trunk. Out of it come small to medium mushrooms, usually a few together in loose troops or tufts rather than a single tight bouquet, with warm ochre to tawny-golden caps and stipes that curve upward from the wood.

The colour is the first hook. Everything about this fungus reads as some shade of yellow-brown: a golden ochre cap, yellowish flesh, pale yellow young gills going to rust. When you turn a mature cap over, the gills are strikingly rusty-orange, and a mature troop often has rusty dust settled on the caps of the lower specimens. That combination of yellow tones plus rust on a conifer stump is the core impression.

Reading the cap

Caps are 2 to 6 cm across, convex at first with an inrolled margin, expanding to broadly convex or flat with a low central hump. The surface is dry, never sticky or glutinous, and this is worth confirming by touch on a damp specimen because it eliminates a whole group of relatives at a stroke.

Look at the surface under a hand lens or in raking light. It is not smooth: the skin breaks up into fine, appressed, darker fibrils and small scurfy scales, densest over the centre and thinning toward the margin, so the cap looks minutely roughened or fibrillose rather than polished. Colour is tawny ochre to golden-brown, usually darker at the disc, and it fades toward buff as the fruitbody dries. Young margins may carry a few pale fibrous veil remnants hanging from the edge.

The gills

The spore-bearing surface here is gills, and they are close to crowded, narrowly attached to the stipe and often with a short decurrent tooth running down it. Their colour progression is the crux of the identification: pale yellow to buff-yellow in a young button, then progressively ochre, then a clear rusty orange-brown at maturity. Older gills are frequently mottled or spotted with darker rusty patches, and the gill edges may look slightly paler and finely uneven under a lens.

Do not confuse rusty gill colour caused by spore maturation with rusty spore dust deposited from a neighbour above. Check an isolated specimen if you can.

The stipe, veil and base

Stipes are 3 to 7 cm long and slender, 3 to 8 mm thick, more or less equal or slightly swollen at the base, often curved because the fruitbody has grown outward from vertical wood. They are yellowish to tawny, paler at the apex, becoming rusty brown from the base upward with age, and clothed in fine longitudinal silky fibrils.

There is a cobwebby partial veil, a cortina, in young specimens, stretching from the cap margin to the stipe. It is fine and fugacious and does not form a membranous ring. What it leaves is a faint fibrillose zone on the upper stipe that catches falling spores and turns rusty, so on a mature specimen you often see a dark rust-coloured band where the ring would have been. The base is usually clothed in whitish to yellowish mycelial down that binds the wood fibres or sawdust.

Flesh and colour change

Cut a fruitbody in half from cap to base. The flesh is thin, pale yellow to yellow-buff, deepening to brownish in the stipe base. There is no milky exudate and no rapid bruising colour change to speak of, though handled surfaces may slowly discolour rustier. A drop of alkali on the cap surface produces a darker reaction in some collections; note it if you carry chemicals, but the field identification does not depend on it.

Taking and reading a spore print

Getting a print is the most decisive single step and should be routine here. Cut the stipe flush with the gills, set the cap gill-side down on white paper, cover it with a cup or box to stop draughts, and leave it four to eight hours or overnight. Use white paper, not black, because the point is to judge the exact tone of a mid-coloured deposit.

The print reads bright rusty orange-brown, warmer and more orange than the dull snuff-brown of an Inocybe and completely different from the purple-black of a Hypholoma. Under a microscope the spores are ellipsoid to almond-shaped, roughened with fine warts, lack a germ pore, and turn reddish-brown in an iodine-based mounting fluid. The warty, pore-less spore is the genus signature.

Substrate and season

This species is a wood decomposer with a strong preference for conifer material: pine, spruce and larch stumps, buried conifer roots, fallen branches, sawdust and old plantation debris. It fruits from late summer through autumn and can persist into early winter in mild spells, and repeat flushes come from the same stump over successive years as the wood breaks down.

Recording the tree genus under which you found it is genuinely useful, because several close relatives in the genus are separated partly by whether the wood is coniferous or broadleaved.

Separating it from the look-alikes

Gymnopilus penetrans and relatives. The commonest confusion, and the difference is cap texture. That species has an essentially smooth, glabrous, silky-shining cap with no scurfy scales, and its gills develop very characteristic discrete rusty spots on a paler ground. Under a lens, a smooth cap versus a finely scaly one is a clear call in fresh material.

Spectacular Rustgill, Gymnopilus junonius. Same rust-orange print and yellow-brown palette, but a completely different scale: caps 8 to 20 cm, growing in massive dense tufts at the base of hardwood trunks and stumps, with a stout stipe swollen in the middle and a well-formed membranous ring.

Pholiota species. These share a brown to rust-brown print and scaly caps, but most of the confusable ones have a distinctly viscid or glutinous cap surface when wet, and the scales are coarser and often recurved rather than fine and appressed. Pholiota squarrosa is dry but has conspicuous upturned pointed scales and grows in large clumps at the foot of broadleaf trees.

Galerina marginata group. Similar size and wood habit, and also rust-brown spored, but the cap is smooth, hygrophanous and two-toned as it dries, and the stipe carries a distinct membranous ring plus a whitish fibrillose coating below it. No scurfy cap scales, and the gill colour is duller brown rather than fiery rust.

Hypholoma species. Similar tufted habit on conifer wood, but the print is purple-brown to blackish, and the gills pass through grey, olive or greenish tones rather than yellow to rust. Getting a print settles it in one step.

Velvet Shank, Flammulina velutipes. Orange and wood-inhabiting, but the cap is smooth and sticky, the stipe becomes velvety blackish-brown, and the spore print is white.

A quick field checklist

Conifer wood, tawny-golden dry cap with fine appressed scales, yellow gills turning rusty with a decurrent tooth, fibrillose yellow stipe with a rusty cortina zone and no membranous ring, yellow flesh, and a bright rust-orange spore print.